diff --git a/app/assets/javascripts/discourse/app/components/d-editor.js b/app/assets/javascripts/discourse/app/components/d-editor.js
index 80e63ce8fbe..81dddeda768 100644
--- a/app/assets/javascripts/discourse/app/components/d-editor.js
+++ b/app/assets/javascripts/discourse/app/components/d-editor.js
@@ -35,29 +35,15 @@ import { siteDir } from "discourse/lib/text-direction";
 import { translations } from "pretty-text/emoji/data";
 import { wantsNewWindow } from "discourse/lib/intercept-click";
 import { action } from "@ember/object";
-import TextareaTextManipulation from "discourse/mixins/textarea-text-manipulation";
-
-// Our head can be a static string or a function that returns a string
-// based on input (like for numbered lists).
-function getHead(head, prev) {
-  if (typeof head === "string") {
-    return [head, head.length];
-  } else {
-    return getHead(head(prev));
-  }
-}
+import TextareaTextManipulation, {
+  getHead,
+} from "discourse/mixins/textarea-text-manipulation";
 
 function getButtonLabel(labelKey, defaultLabel) {
   // use the Font Awesome icon if the label matches the default
   return I18n.t(labelKey) === defaultLabel ? null : labelKey;
 }
 
-const OP = {
-  NONE: 0,
-  REMOVED: 1,
-  ADDED: 2,
-};
-
 const FOUR_SPACES_INDENT = "4-spaces-indent";
 
 let _createCallbacks = [];
@@ -285,8 +271,8 @@ export default Component.extend(TextareaTextManipulation, {
       });
     });
 
-    this._itsatrap.bind("tab", () => this._indentSelection("right"));
-    this._itsatrap.bind("shift+tab", () => this._indentSelection("left"));
+    this._itsatrap.bind("tab", () => this.indentSelection("right"));
+    this._itsatrap.bind("shift+tab", () => this.indentSelection("left"));
 
     // disable clicking on links in the preview
     this.element
@@ -294,13 +280,13 @@ export default Component.extend(TextareaTextManipulation, {
       .addEventListener("click", this._handlePreviewLinkClick);
 
     if (this.composerEvents) {
-      this.appEvents.on("composer:insert-block", this, "_insertBlock");
-      this.appEvents.on("composer:insert-text", this, "_insertText");
-      this.appEvents.on("composer:replace-text", this, "_replaceText");
+      this.appEvents.on("composer:insert-block", this, "insertBlock");
+      this.appEvents.on("composer:insert-text", this, "insertText");
+      this.appEvents.on("composer:replace-text", this, "replaceText");
       this.appEvents.on(
         "composer:indent-selected-text",
         this,
-        "_indentSelection"
+        "indentSelection"
       );
     }
 
@@ -338,13 +324,13 @@ export default Component.extend(TextareaTextManipulation, {
   @on("willDestroyElement")
   _shutDown() {
     if (this.composerEvents) {
-      this.appEvents.off("composer:insert-block", this, "_insertBlock");
-      this.appEvents.off("composer:insert-text", this, "_insertText");
-      this.appEvents.off("composer:replace-text", this, "_replaceText");
+      this.appEvents.off("composer:insert-block", this, "insertBlock");
+      this.appEvents.off("composer:insert-text", this, "insertText");
+      this.appEvents.off("composer:replace-text", this, "replaceText");
       this.appEvents.off(
         "composer:indent-selected-text",
         this,
-        "_indentSelection"
+        "indentSelection"
       );
     }
 
@@ -477,7 +463,7 @@ export default Component.extend(TextareaTextManipulation, {
       key: "#",
       afterComplete: (value) => {
         this.set("value", value);
-        schedule("afterRender", this, this._focusTextArea);
+        schedule("afterRender", this, this.focusTextArea);
       },
       transformComplete: (obj) => {
         return obj.text;
@@ -504,7 +490,7 @@ export default Component.extend(TextareaTextManipulation, {
       key: ":",
       afterComplete: (text) => {
         this.set("value", text);
-        schedule("afterRender", this, this._focusTextArea);
+        schedule("afterRender", this, this.focusTextArea);
       },
 
       onKeyUp: (text, cp) => {
@@ -617,117 +603,9 @@ export default Component.extend(TextareaTextManipulation, {
     });
   },
 
-  // perform the same operation over many lines of text
-  _getMultilineContents(lines, head, hval, hlen, tail, tlen, opts) {
-    let operation = OP.NONE;
-
-    const applyEmptyLines = opts && opts.applyEmptyLines;
-
-    return lines
-      .map((l) => {
-        if (!applyEmptyLines && l.length === 0) {
-          return l;
-        }
-
-        if (
-          operation !== OP.ADDED &&
-          ((l.slice(0, hlen) === hval && tlen === 0) ||
-            (tail.length && l.slice(-tlen) === tail))
-        ) {
-          operation = OP.REMOVED;
-          if (tlen === 0) {
-            const result = l.slice(hlen);
-            [hval, hlen] = getHead(head, hval);
-            return result;
-          } else if (l.slice(-tlen) === tail) {
-            const result = l.slice(hlen, -tlen);
-            [hval, hlen] = getHead(head, hval);
-            return result;
-          }
-        } else if (operation === OP.NONE) {
-          operation = OP.ADDED;
-        } else if (operation === OP.REMOVED) {
-          return l;
-        }
-
-        const result = `${hval}${l}${tail}`;
-        [hval, hlen] = getHead(head, hval);
-        return result;
-      })
-      .join("\n");
-  },
-
-  _applySurround(sel, head, tail, exampleKey, opts) {
-    const pre = sel.pre;
-    const post = sel.post;
-
-    const tlen = tail.length;
-    if (sel.start === sel.end) {
-      if (tlen === 0) {
-        return;
-      }
-
-      const [hval, hlen] = getHead(head);
-      const example = I18n.t(`composer.${exampleKey}`);
-      this.set("value", `${pre}${hval}${example}${tail}${post}`);
-      this._selectText(pre.length + hlen, example.length);
-    } else if (opts && !opts.multiline) {
-      let [hval, hlen] = getHead(head);
-
-      if (opts.useBlockMode && sel.value.split("\n").length > 1) {
-        hval += "\n";
-        hlen += 1;
-        tail = `\n${tail}`;
-      }
-
-      if (pre.slice(-hlen) === hval && post.slice(0, tail.length) === tail) {
-        this.set(
-          "value",
-          `${pre.slice(0, -hlen)}${sel.value}${post.slice(tail.length)}`
-        );
-        this._selectText(sel.start - hlen, sel.value.length);
-      } else {
-        this.set("value", `${pre}${hval}${sel.value}${tail}${post}`);
-        this._selectText(sel.start + hlen, sel.value.length);
-      }
-    } else {
-      const lines = sel.value.split("\n");
-
-      let [hval, hlen] = getHead(head);
-      if (
-        lines.length === 1 &&
-        pre.slice(-tlen) === tail &&
-        post.slice(0, hlen) === hval
-      ) {
-        this.set(
-          "value",
-          `${pre.slice(0, -hlen)}${sel.value}${post.slice(tlen)}`
-        );
-        this._selectText(sel.start - hlen, sel.value.length);
-      } else {
-        const contents = this._getMultilineContents(
-          lines,
-          head,
-          hval,
-          hlen,
-          tail,
-          tlen,
-          opts
-        );
-
-        this.set("value", `${pre}${contents}${post}`);
-        if (lines.length === 1 && tlen > 0) {
-          this._selectText(sel.start + hlen, sel.value.length);
-        } else {
-          this._selectText(sel.start, contents.length);
-        }
-      }
-    }
-  },
-
   _applyList(sel, head, exampleKey, opts) {
     if (sel.value.indexOf("\n") !== -1) {
-      this._applySurround(sel, head, "", exampleKey, opts);
+      this.applySurround(sel, head, "", exampleKey, opts);
     } else {
       const [hval, hlen] = getHead(head);
       if (sel.start === sel.end) {
@@ -745,7 +623,7 @@ export default Component.extend(TextareaTextManipulation, {
       const post = trimmedPost.length ? `\n\n${trimmedPost}` : trimmedPost;
 
       this.set("value", `${preLines}${number}${post}`);
-      this._selectText(preLines.length, number.length);
+      this.selectText(preLines.length, number.length);
     }
   },
 
@@ -811,16 +689,16 @@ export default Component.extend(TextareaTextManipulation, {
         return;
       }
 
-      const selected = this._getSelected(button.trimLeading);
+      const selected = this.getSelected(button.trimLeading);
       const toolbarEvent = {
         selected,
         selectText: (from, length) =>
-          this._selectText(from, length, { scroll: false }),
+          this.selectText(from, length, { scroll: false }),
         applySurround: (head, tail, exampleKey, opts) =>
-          this._applySurround(selected, head, tail, exampleKey, opts),
+          this.applySurround(selected, head, tail, exampleKey, opts),
         applyList: (head, exampleKey, opts) =>
           this._applyList(selected, head, exampleKey, opts),
-        addText: (text) => this._addText(selected, text),
+        addText: (text) => this.addText(selected, text),
         getText: () => this.value,
         toggleDirection: () => this._toggleDirection(),
       };
@@ -855,7 +733,7 @@ export default Component.extend(TextareaTextManipulation, {
         return;
       }
 
-      const sel = this._getSelected("", { lineVal: true });
+      const sel = this.getSelected("", { lineVal: true });
       const selValue = sel.value;
       const hasNewLine = selValue.indexOf("\n") !== -1;
       const isBlankLine = sel.lineVal.trim().length === 0;
@@ -867,25 +745,20 @@ export default Component.extend(TextareaTextManipulation, {
           if (isFourSpacesIndent) {
             const example = I18n.t(`composer.code_text`);
             this.set("value", `${sel.pre}    ${example}${sel.post}`);
-            return this._selectText(sel.pre.length + 4, example.length);
+            return this.selectText(sel.pre.length + 4, example.length);
           } else {
-            return this._applySurround(
-              sel,
-              "```\n",
-              "\n```",
-              "paste_code_text"
-            );
+            return this.applySurround(sel, "```\n", "\n```", "paste_code_text");
           }
         } else {
-          return this._applySurround(sel, "`", "`", "code_title");
+          return this.applySurround(sel, "`", "`", "code_title");
         }
       } else {
         if (isFourSpacesIndent) {
-          return this._applySurround(sel, "    ", "", "code_text");
+          return this.applySurround(sel, "    ", "", "code_text");
         } else {
           const preNewline = sel.pre[-1] !== "\n" && sel.pre !== "" ? "\n" : "";
           const postNewline = sel.post[0] !== "\n" ? "\n" : "";
-          return this._addText(
+          return this.addText(
             sel,
             `${preNewline}\`\`\`\n${sel.value}\n\`\`\`${postNewline}`
           );
diff --git a/app/assets/javascripts/discourse/app/mixins/textarea-text-manipulation.js b/app/assets/javascripts/discourse/app/mixins/textarea-text-manipulation.js
index 896cfd9aeae..3a62254fdbc 100644
--- a/app/assets/javascripts/discourse/app/mixins/textarea-text-manipulation.js
+++ b/app/assets/javascripts/discourse/app/mixins/textarea-text-manipulation.js
@@ -1,4 +1,5 @@
 import { bind } from "discourse-common/utils/decorators";
+import I18n from "I18n";
 import Mixin from "@ember/object/mixin";
 import { generateLinkifyFunction } from "discourse/lib/text";
 import toMarkdown from "discourse/lib/to-markdown";
@@ -14,6 +15,22 @@ import { next, schedule } from "@ember/runloop";
 const INDENT_DIRECTION_LEFT = "left";
 const INDENT_DIRECTION_RIGHT = "right";
 
+const OP = {
+  NONE: 0,
+  REMOVED: 1,
+  ADDED: 2,
+};
+
+// Our head can be a static string or a function that returns a string
+// based on input (like for numbered lists).
+export function getHead(head, prev) {
+  if (typeof head === "string") {
+    return [head, head.length];
+  } else {
+    return getHead(head(prev));
+  }
+}
+
 export default Mixin.create({
   init() {
     this._super(...arguments);
@@ -24,6 +41,13 @@ export default Mixin.create({
   },
 
   // ensures textarea scroll position is correct
+  //
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  focusTextArea() {
+    this._focusTextArea();
+  },
+
   _focusTextArea() {
     if (!this.element || this.isDestroying || this.isDestroyed) {
       return;
@@ -37,12 +61,30 @@ export default Mixin.create({
     this._textarea.focus();
   },
 
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  insertBlock(text) {
+    this._insertBlock(text);
+  },
+
   _insertBlock(text) {
-    this._addBlock(this._getSelected(), text);
+    this._addBlock(this.getSelected(), text);
+  },
+
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  insertText(text, options) {
+    this._insertText(text, options);
   },
 
   _insertText(text, options) {
-    this._addText(this._getSelected(), text, options);
+    this._addText(this.getSelected(), text, options);
+  },
+
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  getSelected(trimLeading, opts) {
+    return this._getSelected(trimLeading, opts);
   },
 
   _getSelected(trimLeading, opts) {
@@ -80,6 +122,12 @@ export default Mixin.create({
     }
   },
 
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  selectText(from, length, opts = { scroll: true }) {
+    this._selectText(from, length, opts);
+  },
+
   _selectText(from, length, opts = { scroll: true }) {
     next(() => {
       if (!this.element) {
@@ -99,6 +147,12 @@ export default Mixin.create({
     });
   },
 
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  replaceText(oldVal, newVal, opts = {}) {
+    this._replaceText(oldVal, newVal, opts);
+  },
+
   _replaceText(oldVal, newVal, opts = {}) {
     const val = this.value;
     const needleStart = val.indexOf(oldVal);
@@ -135,13 +189,127 @@ export default Mixin.create({
       !opts.skipNewSelection
     ) {
       // Restore cursor.
-      this._selectText(
+      this.selectText(
         newSelection.start,
         newSelection.end - newSelection.start
       );
     }
   },
 
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  applySurround(sel, head, tail, exampleKey, opts) {
+    this._applySurround(sel, head, tail, exampleKey, opts);
+  },
+
+  _applySurround(sel, head, tail, exampleKey, opts) {
+    const pre = sel.pre;
+    const post = sel.post;
+
+    const tlen = tail.length;
+    if (sel.start === sel.end) {
+      if (tlen === 0) {
+        return;
+      }
+
+      const [hval, hlen] = getHead(head);
+      const example = I18n.t(`composer.${exampleKey}`);
+      this.set("value", `${pre}${hval}${example}${tail}${post}`);
+      this.selectText(pre.length + hlen, example.length);
+    } else if (opts && !opts.multiline) {
+      let [hval, hlen] = getHead(head);
+
+      if (opts.useBlockMode && sel.value.split("\n").length > 1) {
+        hval += "\n";
+        hlen += 1;
+        tail = `\n${tail}`;
+      }
+
+      if (pre.slice(-hlen) === hval && post.slice(0, tail.length) === tail) {
+        this.set(
+          "value",
+          `${pre.slice(0, -hlen)}${sel.value}${post.slice(tail.length)}`
+        );
+        this.selectText(sel.start - hlen, sel.value.length);
+      } else {
+        this.set("value", `${pre}${hval}${sel.value}${tail}${post}`);
+        this.selectText(sel.start + hlen, sel.value.length);
+      }
+    } else {
+      const lines = sel.value.split("\n");
+
+      let [hval, hlen] = getHead(head);
+      if (
+        lines.length === 1 &&
+        pre.slice(-tlen) === tail &&
+        post.slice(0, hlen) === hval
+      ) {
+        this.set(
+          "value",
+          `${pre.slice(0, -hlen)}${sel.value}${post.slice(tlen)}`
+        );
+        this.selectText(sel.start - hlen, sel.value.length);
+      } else {
+        const contents = this._getMultilineContents(
+          lines,
+          head,
+          hval,
+          hlen,
+          tail,
+          tlen,
+          opts
+        );
+
+        this.set("value", `${pre}${contents}${post}`);
+        if (lines.length === 1 && tlen > 0) {
+          this.selectText(sel.start + hlen, sel.value.length);
+        } else {
+          this.selectText(sel.start, contents.length);
+        }
+      }
+    }
+  },
+
+  // perform the same operation over many lines of text
+  _getMultilineContents(lines, head, hval, hlen, tail, tlen, opts) {
+    let operation = OP.NONE;
+
+    const applyEmptyLines = opts && opts.applyEmptyLines;
+
+    return lines
+      .map((l) => {
+        if (!applyEmptyLines && l.length === 0) {
+          return l;
+        }
+
+        if (
+          operation !== OP.ADDED &&
+          ((l.slice(0, hlen) === hval && tlen === 0) ||
+            (tail.length && l.slice(-tlen) === tail))
+        ) {
+          operation = OP.REMOVED;
+          if (tlen === 0) {
+            const result = l.slice(hlen);
+            [hval, hlen] = getHead(head, hval);
+            return result;
+          } else if (l.slice(-tlen) === tail) {
+            const result = l.slice(hlen, -tlen);
+            [hval, hlen] = getHead(head, hval);
+            return result;
+          }
+        } else if (operation === OP.NONE) {
+          operation = OP.ADDED;
+        } else if (operation === OP.REMOVED) {
+          return l;
+        }
+
+        const result = `${hval}${l}${tail}`;
+        [hval, hlen] = getHead(head, hval);
+        return result;
+      })
+      .join("\n");
+  },
+
   _addBlock(sel, text) {
     text = (text || "").trim();
     if (text.length === 0) {
@@ -172,6 +340,12 @@ export default Mixin.create({
     schedule("afterRender", this, this._focusTextArea);
   },
 
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  addText(sel, text, options) {
+    this._addText(sel, text, options);
+  },
+
   _addText(sel, text, options) {
     if (options && options.ensureSpace) {
       if ((sel.pre + "").length > 0) {
@@ -196,6 +370,12 @@ export default Mixin.create({
     this._focusTextArea();
   },
 
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  extractTable(text) {
+    return this._extractTable(text);
+  },
+
   _extractTable(text) {
     if (text.endsWith("\n")) {
       text = text.substring(0, text.length - 1);
@@ -233,6 +413,12 @@ export default Mixin.create({
     return null;
   },
 
+  // TODO (martin) clean up this indirection, functions used outside this
+  // file should not be prefixed with lowercase
+  isInside(text, regex) {
+    return this._isInside(text, regex);
+  },
+
   _isInside(text, regex) {
     const matches = text.match(regex);
     return matches && matches.length % 2;
@@ -254,7 +440,7 @@ export default Mixin.create({
     let html = clipboard.getData("text/html");
     let handled = false;
 
-    const selected = this._getSelected(null, { lineVal: true });
+    const selected = this.getSelected(null, { lineVal: true });
     const { pre, value: selectedValue, lineVal } = selected;
     const isInlinePasting = pre.match(/[^\n]$/);
     const isCodeBlock = this._isInside(pre, /(^|\n)```/g);
@@ -349,12 +535,12 @@ export default Mixin.create({
   },
 
   @bind
-  _indentSelection(direction) {
+  indentSelection(direction) {
     if (![INDENT_DIRECTION_LEFT, INDENT_DIRECTION_RIGHT].includes(direction)) {
       return;
     }
 
-    const selected = this._getSelected(null, { lineVal: true });
+    const selected = this.getSelected(null, { lineVal: true });
     const { lineVal } = selected;
     let value = selected.value;
 
@@ -414,14 +600,14 @@ export default Mixin.create({
       .join("\n");
 
     if (newValue.trim() !== "") {
-      this._replaceText(value, newValue, { skipNewSelection: true });
-      this._selectText(this.value.indexOf(newValue), newValue.length);
+      this.replaceText(value, newValue, { skipNewSelection: true });
+      this.selectText(this.value.indexOf(newValue), newValue.length);
     }
   },
 
   @action
   emojiSelected(code) {
-    let selected = this._getSelected();
+    let selected = this.getSelected();
     const captures = selected.pre.match(/\B:(\w*)$/);
 
     if (isEmpty(captures)) {